A large burden of cancer morbidity and mortality is potentially preventable by changes in personal health behaviors. Health behavior advice (HBA) by primary care physicians, who provide basic health care to most Americans, holds great promise as a strategy to alter cancer-related health behaviors and reduce morbidity and mortality. However, major barriers to implementing effective intervention stem from the feasibility of incorporating effective HBA approaches into the competing demands of every day practice and a predominately illness care mode of providing health care. One potentially powerful strategy that has been promoted is the use of illness visits as a 'teachable moment' for health behavior change. However, little is known about the specific communication strategies essential to creating a teachable moment or the effectiveness of this pproach for health behavior change. Understanding the way a teachable moment is constructed through communication and evaluation of the effectiveness of this strategy is both fundamental and crucial to efforts to promote adoption of a teachable moment approach for health behavior change. Therefore, the goal of this multimethod study is to characterize the way a teachable moment arises and is constructed within the patient-physician interaction, and to evaluate the effectiveness of this strategy on patient recall of advice, motivation to modify behavior and change in health behavior. Audio recordings of 800 adult patient-clinician visits from a stratified random sample of 16 community family physicians will provide the rich data for the in-depth qualitative analysis. Conversation analysis will be used to characterize how the 'teachable moment' arises, its structure and the content of the dialogue; and identify contextual features of the visit that may have enabled or impeded the communication of HBA. Key variables derived from the qualitative analysis including elements of the teachable moment, the content of the advice, cues, competing demands and the patient centeredness of the interaction will coded for each of the 800 visits. Longitudinal follow-up of patients with one- and six-month phone follow-up surveys will be used to assess the outcomes of change in motivation to modify behavior and change in health behavior. The effect of a teachable moment strategy on each of the outcomes will be evaluated using multivariable models to include contextual covariates and will use GEE methods to account for the clustered data structure. The findings from this study will move 'teachable moments' from the realm of an appealing idea into an empirically-based strategy for affecting health behavior change and will guide physicians to communicate health behavior advice when it is likely to have the most impact and in a way that is likely to have a significant impact on patient outcomes.